Obtained: During the Chapter 2 Intermission, accept a Topic from Touma then head to Toubo Rooftop and speak to him in person.
When you’re ready, head to Harajuku to meet up with Touma in front of Anzu. As part of a dialog scene, you’ll help Touma wrangle in the girls’ Topics then Touma’s soul will achieve a new awakening. Afterwards, head on over to Bloom Palace to unlock Touma’s Radiant Skill, Door of Transformation.